Many feel the blame lies squarely with the food manufacturers, who have loaded their products with fat and sugar to make them as tasty as possible - swelling millions of bellies and their own coffers at a stroke.

Now, however, major US manufacturer Kraft has announced a package of measures designed to tackle the problem.

The motivation is unclear. The company says it is concerned about levels of obesity, while sceptics believe it is more worried about the growing threat of litigation from people who claim gorging on their products has ruined their life.

Whatever, experts believe that the measures - which include reducing portion size - are a good start. However, they warn that without a concerted effort to improve diet and lifestyle they will have little long term impact.

As Amanda Wynne, of the British Dietetic Association, says: "This is not just about portion size. Just getting somebody to cut down from five biscuits a day to four is not going to tackle obesity, we need a more holistic approach."

Processed foods are popular

Dr Ian Banks, a GP and member of the UK's National Obesity Forum, is even less impressed.

"If portion sizes are cut down, then the temptation must be to buy two instead of one. It may be that people just end up eating more."

However, obesity specialist Professor Stephen Bloom, said it was encouraging that manufacturers had taken a positive step.

"We have got an epidemic of obesity, and at last they are paying attention and taking some action."

And Dr Ian Campbell, chair of the National Obesity Forum campaign group, which
aims to raise awareness of the health risks associated with obesity, said: "Considering that portion sizes have increased by 30% over the last decade, it's about time this trend was reversed."

Children are key

Ms Wynne said the best way to tackle obesity was to target children at an early stage.

She said it was wrong that many products aimed at young people were high in fats and sugars, and said any measure to reduce these ingredients would be welcome.

There is a big difference between finding a small bunch of grapes in your lunchbox, rather than a big, bruised apple

Amanda Wynne

But what was really needed was a campaign to educate young minds - and stomachs.

It was vital to impress on children the need to eat healthily and to take regular exercise.

And that advice should come from teachers or nutritionists - certainly not from the food industry.

Many parents were making efforts to encourage their children to eat healthily, said Ms Wynne. But, unfortunately, some shot themselves in the foot, by providing unappetising fare.

"Children need to learn that healthy food can also be tasty food," she said.

"For instance, there is a big difference between finding a small bunch of grapes in your lunchbox, rather than a big, bruised apple."

It was also important for young people to develop good cooking skills.

Older targets

Tackling obesity in adults was a much tougher proposition, said Ms Wynne, because bad habits are so much more ingrained.

But just because middle-aged people are set in their ways is no reason to give up on them.

"We need to make it easier for everybody to take exercise," she said.

"This might mean making it easier to get access to a gym, or it might mean simple things like making sure that pavements and parks are safe and well lit so that more people can be tempted to go for a walk in the evenings."

Dr Banks said doctors also had a significant role to play in helping people to understand the risks associated with being overweight.

However, he warned that a sanctimonious approach wouldn't work.

"For men in particular simply preaching at them is very, very bad.

"There is no point in simply saying 'you must cut down on calories and fat'.

"A little bit of digging may uncover underlying reasons why people find it so hard to lose weight, and which may help the doctor to offer a structured approach that is relevant to their circumstances, and which may actually work."